Substructure and dispersion hardening in aged, cold worked, and annealed Al-4 wt pct Cu alloy
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AND
J. A. LUND
E l e c t r o n m i c r o s c o p y and X - r a y line p r o f i l e a n a l y s e s have been e m p l o y e d to define the m i c r o s t r u c t u r e s and s u b s t r u c t u r e s of p u r e a l u m i n u m and an o v e r a g e d A1-4 wt p e t Cu a l l o y a f t e r v a r i o u s t h e r m o m e c h a n i c a l t r e a t m e n t s . T e n s i l e t e s t s w e r e p e r f o r m e d on the s a m e m a t e r i a l s , and the r e s u l t s have been i n t e r p r e t e d in t e r m s of s t r u c t u r e . A given cold r o l l i n g r e d u c t i o n of the aged A1-4 wt p e t Cu a l l o y p r o d u c e d a much h i g h e r d i s l o c a t i o n d e n s i t y and a l e s s c e l l u l a r s u b s t r u c t u r e than the s a m e t r e a t m e n t p r o d u c e d in p u r e a l u m i n u m of c o m p a r a b l e i n i t i a l g r a i n s i z e . A n n e a l i n g a f t e r cold w o r k p r o d u c e d s i m i l a r r e s p o n s e s in both the p u r e m e t a l and the a l l o y . F o r the aged a l l o y in the a s - r o l l e d , or r o l l e d - a n d - a n n e a l e d c o n d i t i o n , d i s p e r s i o n s t r e n g t h e n i n g and s u b s t r u c t u r e s t r e n g t h e n i n g w e r e found to be l i n e a r l y a d d i t i v e , and they a c c o u n t e d for v i r t u a l l y a l l the o b s e r v e d t e n s i l e y i e l d s t r e n g t h . S u b s t r u c t u r e s t r e n g t h e n i n g has been d i s c u s s e d in t e r m s of the r e l a t i o n between d i s l o c a t i o n d e n s i t y and the s p a c i n g and n a t u r e of the s u b s t r u c t u r e b o u n d a r i e s ,
DURING
the f a b r i c a t i o n of w r o u g h t f o r m s of oxide d i s p e r s i o n - s t r e n g t h e n e d a l l o y s such a s SAP (A1-A1203) o r TD N i c k e l (Ni-ThO2), d e n s e d i s l o c a t i o n s u b s t r u c t u r e s a r e i n t r o d u c e d . A p p a r e n t l y due to an a n c h o r i n g e f f e c t of the d i s p e r s e d oxide p a r t i c l e s on p a r t s of the s u b s t r u c t u r e , t h e s e a l l o y s a r e r e s i s t a n t to the e f f e c t s of a n n e a l i n g a f t e r f a b r i c a t i o n or f u r t h e r cold w o r k , and they t y p i c a l l y r e s i s t r e c r y s t a l l i z a t i o n at high f r a c t i o n s of t h e i r a b s o l u t e m e l t i n g t e m p e r a t u r e s . H a n s e n s t u d i e d the s t r u c t u r e s and 20~ t e n s i l e p r o p e r t i e s of A1-A1203 a l l o y s in the hot e x t r u d e d I and in the cold w o r k e d and a n n e a l e d 2 c o n d i t i o n s . He concluded that d i s p e r s i o n s t r e n g t h e n i n g due to the oxide p a r t i c l e s and s u b g r a i n or c e l l b o u n d a r y s t r e n g t h e n i n g w e r e l i n e a r l y a d d i t i v e in a l l c o n d i t i o n s . The p r e s e n t w o r k w a s u n d e r t a k e n to c o m p a r e with A1-A1203 the r e s p o n s e to t h e r m o m e c h a n i c a l t r e a t m e n t of an a l u m i n u m a l l o y containing a d i s p e r s i o
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